Re: changing the classpath at runtime in code

From:
=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>
Newsgroups:
comp.lang.java.programmer
Date:
Wed, 24 Oct 2007 21:13:14 -0400
Message-ID:
<471fed9d$0$90273$14726298@news.sunsite.dk>
Aryeh M. Friedman wrote:

On Oct 24, 8:16 pm, Arne VajhHj <a...@vajhoej.dk> wrote:

Aryeh M. Friedman wrote:

Is it possible for a java app to change it's classpath at runtime. I
tried:
System.setProperty("java.class.path","foo")
The reason for wanting to try is URLClassLoader will not physically
reread a class file if it is in the classpath.

Create a URLClassLoader with a url that are *not* in the parent
classloaders url's.


so just do:

URL[] url={new URL("file://foo")};
URLClassLoader laoder=new URLClassLoader(url);
?


I have a little demo example I often use to illustrate
(subdir test is not in classpath of program).

Arne

===============================

import java.io.*;
import java.net.*;

public class DoubleDynmaic {
    private static void dynno(int n) {
       (new File("test")).mkdir();
       try {
          OutputStream os = new FileOutputStream("test/Test.java");
          PrintStream ps = new PrintStream(os);
          ps.println("public class Test {");
          ps.println(" public Test() {");
          ps.println(" System.out.println(" + n + ");");
          ps.println(" }");
          ps.println("}");
          ps.close();
          os.close();
          Runtime.getRuntime().exec("javac -d test
test/Test.java").waitFor();
          URL[] url = new URL[1];
          url[0] = new URL("file:test/");
          URLClassLoader cl = new URLClassLoader(url);
          Class.forName("Test", true, cl).newInstance();
       } catch (Exception e) {
          e.printStackTrace();
       }
    }
    public static void main(String[] args) {
       for(int i = 0; i < 10; i++) {
          dynno(i);
       }
    }
}

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